This invention relates to a process for liquefying coal or similar solid carbonaceous fuels. More particularly, this invention relates to a coal liquefaction process employing process derived hydrogen-rich gas made by the partial oxidation of purge and vent hydrogen-containing gases, optionally in admixture with a vacuum bottom stream containing ash.
Coal will emerge as an increasingly important energy source by the end of the decade. It has been predicted that by 1990, the consumption of coal among western industrialized nations will have grown by 47%. There are ample coal supplies in the United States, Canada, and Australia to meet this growing demand. Liquefaction of coal to produce liquid fuels and chemical by-products will become increasingly important, especially when petroleum supplies become uncertain.
Methods for producing hydrocarbonaceous liquids by the solvent extraction of coal and similar carbonaceous materials are well known. Both catalytic and non-catalytic processes have been devised for digesting the coal in a coal hydrogenation reactor. For example, reference is made to U.S. Pat. Nos. 3,477,941; 3,519,553; 3,519,554; 3,519,555; 3,867,275; and 4,189,371.
Hydrogen for the hydrogenation reactor in these systems is commonly made by the catalytic steam reforming of natural gas or gaseous ends. However, this is uneconomical since either an additional pure gaseous fuel must be imported into the system, or costly gas purification is required before the gaseous ends may be used in the catalytic steam reformer. Also, the yield of such gaseous fuels after purification may be insufficient to produce the required amount of hydrogen. The multihydrotorting of coal-water slurries with gaseous mixtures comprising H.sub.2 +CO as produced by the partial oxidation of coal char is described in coassigned U.S. Pat. Nos. 3,715,195 and 3,715,301. The partial oxidation of slurries of oil, water and unconverted carbon is described in coassigned U.S. Pat. No. 3,528,930. While the partial oxidation of coal or liquefaction bottoms has been accomplished, the cost of the steam temperature moderator may be an economic penalty. Further, it would be uneconomical to burn up substantial amounts of the feed coal or the valuable liquid hydrocarbon products to make hydrogen. Also, there would still remain the problem and cost of disposing of the noxious vent and purge gases produced in the liquefaction step.
In the subject process, preferably no supplemental water or steam is required; and the noxious vent and purge gases are readily disposed of in the gas generator in an environmentally acceptable manner.
Advantageously, by the subject process catalytic steam reforming requiring costly gas purification steps is eliminated. Noxious vent and purge gas streams and optionally high ash-containing vacuum bottom streams may now be advantageously used as feedstock to obtain hydrogen for use in the subject solvent coal liquefaction process.